The present invention relates to a device and a method for operating an electric machine. In particular, the present invention relates to a device and a method for operating an electric machine for the transition from a regulated operating mode to a freewheeling mode.
Electric machines, for example, permanently excited synchronous machines, are used in a variety of technical areas. For example, such permanently excited synchronous machines are used in motor vehicles. For safety reasons, previsions must be made for an operating state in the event of a fault. One possibility for setting such an operating state is the so-called freewheeling state. In this case, all terminals of the electric machine are disconnected from each other, and there is no active driving of the electric machine with a voltage. Another safe operating state is the so-called active short circuit. In this case, the terminals of the electric machine are short-circuited with the aid of suitable switching elements.
The German patent application DE 10 2012 010 508 A1 discloses a device and a method for short-circuiting a permanently excited synchronous machine, in which the machine is short-circuited via power converter valves. If a voltage in an intermediate circuit of the drive circuit of the electric machine deviates from a threshold value, the power converter valves are re-opened, and the machine is subsequently operated in the freewheeling state.
Thus, there is a need for a device and a method for operating an electric machine which enables an improved transition from the regulated operating mode to the freewheeling state.